Spark plug electrode seal



June 30, 1964 K. SCHWARTZWALDER 3,139,553

SPARK PLUG ELECTRODE SEAL Filed Nov. 18, 1960 JNVENTOR.

Karl Sabwarkwalder ATTORNEY United States Patent 3,139,553 SPARK PLUG ELECTRODE SEAL Karl Schwartzwalder, Holly, Mich., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Filed Nov. 18, 1960, Ser. No. 70,293 4 Claims. (Cl. 313--144) 'Ilhis invention pertains to spark plugs, and particularly to an improved internal seal between a metal electrode and a ceramic insulator.

Heretofore gas-tight electrically conductive seals of ceramic material have been used to secure center electrodes of spark plugs in their insulators. Thus, in Patent No. 2,106,578 a ceramic seal consisting of a fused mixture of powdered glass and graphite is disclosed, and in Patent No. 2,248,415 a ceramic seal consisting of a fused mixture of powdered glass and powdered metal is disclosed. One of. the inherent deficiencies of the aforementioned conductive ceramic seals is that the glass and conductive powders have only been mechanical mixtures, and in order to obtain a continuous film of metal to form a conductive path between portions of the center electrode structure it is necessary to flow the heated mixture and hot press an electrode portion thereinto. This invention relates. to an improved conductive ceramic seal wherein the glass particles are coated with the conductive metal prior to the fusing operation.

Accordingly, among my objects are the provision of an improved conductive ceramic seal for spark plugs; the further provision of an improved mixture for use as an internal conductive spark plug seal comprising metal coated glass particles; the still further provision of a spark plug embodying an improved ceramic conductive seal comprising metal coated glass particles which are intimately bonded to the spark plug insulator and the center electrode.

The aforementioned and other objects are accomplished in the present invention by utilizing metal coated glass particles comprising at least 50% glass and the remainder metal. Specifically glass particles having a relatively low coefficient of expansion, such as borosilicate glass, commonly known as Pyrex, and having a particle size which will pass through a 28 to a +100 mesh screen are coated with metal, such as nickel. The metal coated glass particles are held together by a small amount of any suitable binder which, of course, is driven off in the fusing operation. A pellet of the metal-glass combination is interposed between spaced portions of the center electrode assembly and heated to a temperature sufiicient to soften or render plastic the sealing material after which one electrode portion is forced into the insulator centerbore to form a gas-tight conductive ceramic seal.

Further objects and advantages of the invention will be apparent from the following description, reference be ing had to the accompanying drawing comprising a side view of a spark plug embodying the improved conductive ceramic seal shown partly in section and partly in elevation, and wherein a preferred embodiment of the present invention is clearly shown.

With particular reference to the drawing, a spark plug is shown comprising a tubular metal shell carrying a ground electrode 12 and enclosing the lower portion of a ceramic insulator 14. A metal shielding barrel 16 is suitably secured to the metal shell 10 and is spaced coaxially of and encloses the upper end of the ceramic insulator 14. The ceramic insulator 14 is suitably secured in position within the shell 10 and the shielding barrel 16 upon assembly of the shielding barrel 16 with the shell 10, upper and lower sea-ling gaskets 18 and 20 being interposed between juxtaposed shoulders of the ceramic "ice insulator and the metal shell and shielding barrel assembly.

The ceramic insulator 14 can be made of various refractory oxides and mixtures of oxides and other ceramic materials which are sintered at high temperatures; for example, the ceramic insulator may be composed of sintered alumina. The insulator 14 is formed with a centerbore of stepped diameter including a smaller diameter lower portion 22 and a larger diameter upper portion 24. A center electrode spindle 26 is disposed Within the smaller diameter portion 22 of the centerbore and has a firing tip protruding from the lower end of the insulator so as to form a spark gap with the ground electrode 12. The spindle 26- may conveniently be composed of nickel and has an upper flange 28 with a slotted head 30, flange 28 abutting an internal shoulder 31 formed between the larger and smaller diameter portions of the stepped centerbore in the insulator. The center electrode assembly also includes a metal contact plug 32 having a threaded shank portion with a notched end 33 which is received in the larger diameter portion 24 of the insulator centerbore. The contact plug 32 is adapted to be engaged by a suitable electrical condnctor which extends through the upper end of the tubular shielding barrel 16 and the tubular upper end of the insulator.

The slotted head 30 on the spindle 26 and the slotted portion 33 of the contact cap 32 are provided to assure a mechanical interlock between these portions of the center electrode assembly and the improved conductive ceramic seal 34, which is the subject matter of this invention.

As alluded to hereinbe-fore, the improved conductive ceramic seal 34 comprises metal coated glass particles of a size which pass through a -28 to a mesh screen, the glass metal combination having a composition in which the metal does not exceed the glass. Various metals may be used to coat the glass particles, such as copper, cobalt, nickel, iron, molybdenum or tungsten. However, nickel is the preferred coating material, whereas the glass is of the borosilicate type, commonly known as Pyrex. The metal coated glass particles are mixed with a suitable binder such as dextrine and Dritex which is driven off in the fusing operation. After the metal coated glass particles have been mixed with the binder, they may conveniently be formed as pellets and placed on top of the electrode spindle 26. Thereafter the contact cap 32 is placed on top of the pellet and the ceramic insulator is heated to a temperature sufiicient to soften or render plastic the scaling material 34. The contact cap 32 is then forced downwardly into the centerbore of the insulator causing the sealing material to be extruded into the position shown in the drawing. The pressure required may be on the order of psi. The threads on the contact cap, as shown in the drawing, do not engage the insulator but merely serve as anchorages for the conductive ceramic seal. At the temperatures employed, i.e., between 1650 F. and 1750 F., the metal coated glass particles unite and also bond to the ceramic insulator and the center electrode portions, firmly anchoring them in the centerbore of the insulator, and producing a gas-tight joint under all normal temperature and pressure conditions encountered in service.

It is important to note that in the interest of both economy and a satisfactory seal, the proportion of metal in the glass-metal combination should not exceed 50% by glass seal is depicted as applied to securing a two-piece electrode to an insulator, this is only exemplary and is not to be construed by way of limitation since it is obvious that the improved conductive ceramic seal is equally useful in securing a single piece center electrode in place as Well as in the manufacture of other articles in which ceramic pants are secured to each other or to metal parts.

The term fused as used herein is intended to encompass softening up to and including liquefaction and the phrase fused mass connotes any material which has been so treated but has subsequently hardened.

It will be understood that while the invention has been described specifically with reference to a preferred embodiment thereof, changes and modifications may be made all Within the full and intended scope of the claims which follow.

I claim:

1. A spark plug comprising a ceramic insulator having a bore therethrough and a hermetic seal of high electrical conductivity in said bore, said seal consisting essentially of a substantially nonporous mass of ceramic and metal and made by applying heat and pressure to a charge of metal-coated ceramic particles inserted into said centerbore to thereby cause said charge to fuse and bond to said insulator.

2. A spark plug comprising a ceramic insulator having a bore therethrough and a hermetic seal of high electrical conductivity in said bore, said seal consisting essentially of a substantially nonporous mass of borosilicate glass and metal and made by applying heat and pressure to a charge of metal-coated borosilicate glass particles inserted into said centerbore to thereby cause said charge to fuse and bond to said insulator.

3. A spark plug as set forth in claim 2 wherein said metal is nickel.

4. A spark plug comprising a ceramic insulator having a bore therethrough with spaced metal members therein and a hermetic seal of high electrical conductivity in said bore between said metal members, said seal consisting essentially of a substantially nonporous mass of at least by weight glass and the remainder metal and made by applying heat and pressure to a charge of metal-coated glass particles inserted into said centerbore to thereby cause said dha-rge to fuse and bond to said insulator.

References Cited in the file of this patent UNITED STATES PATENTS 1,922,221 Steenbeck et al. Aug. 15, 1933 2,248,415 Schwartzwalder et al. July 8, 1941 2,459,282 McDougal et al. Ian. 18, 1949 

1. A SPARK PLUG COMPRISING A CERAMIC INSULATOR HAVING A BORE THERETHROUGH AND A HERMETIC SEAL OF HIGH ELECTRICAL CONDUCTIVITY IN SAID BORE, SAID SEAL CONSISTING ESSENTIALLY OF A SUBSTANTIALLY NONPOROUS MASS OF CERAMIC AND METAL AND MADE BY APPLYING HEAT AND PRESSURE TO A CHARGE OF METAL-COATED CERAMIC PARTICLES INSERTED INTO SAID CENTERBORE TO THEREBY CAUSE SAID CHARGE TO FUSE AND BOND TO SAID INSULATOR. 